Surface and passive/active air mould sampling: A testing exercise in a North London housing estate

Abstract

Despite indoor mould being one of the most common problems in residential properties in the UK, there are not any widely accepted methodologies for its measurement. This paper focusses on this problem of measurement and reports on the findings from a rigorous testing scheme carried out to quantify air and surface mould concentrations and particle counts within 71 rooms from 64 properties in North London, some with and some without visible mould. The aim was to investigate the potential of passive and active air sampling strategies (sampling from still and actively mixed air, respectively) to explain visible mould, and understand how home/room characteristics correlate with the obtained readings. Airborne mould levels were quantified using an Andersen sampler (passively and actively), as well as by a chemical method based on the quantification of the N-acetylhexosaminidase (NAHA) activity (actively), which was also used to quantify surface mould. The mould levels were then correlated against physical characteristics of the tested homes/rooms, collected by means of survey sheets developed as part of this study. The findings did not reveal any independent variable governing all or most of the response variables, but a complex analysis suggested that whether it is a house or a flat could depict mould levels in the air and on the surfaces. It was also shown that a robust testing protocol should combine air and surface based methods, and an active air sampling strategy leads to a more accurate appraisal of airborne mould levels. Finally, the results showed that while there is some correlation between visible mould (and other moisture induced problems such as condensation) and measured air mould concentrations, lack of visible mould within a room does not necessarily mean low air mould concentrations, and thus one should not rely solely on visual inspection.

Indoor mould testing in a historic building: Blickling Hall

“…The NAHA activity values (known also as Mycometer values) (Table 2) show that all rooms tested in this study had very low airborne mould concentrations. According to the benchmarks recently developed for the UK building stock and for the same testing protocol as the one used here, NAHA activity values above 1700 RFU could be indicative of mould growth and therefore require further investigation of the space for a mould source [26]. While left unmeasured, the visual evidence suggests that basement should exhibit much higher airborne mould concentrations.…”

“…settled dust on surfaces. Active sampling, on the other hand, uses active mixing of the air in the room to be tested-it will suspend settled dust so its mould activity can be characterised, and has previously been shown to be strongly correlated to the presence of visible mould and other moisture induced problems within the space [11]. In this study, an active air sampling strategy was adopted for its ability to rule out the impact of the prior disturbance (or lack of it) within the space on the readings [26–28].…”

“…Active sampling, on the other hand, uses active mixing of the air in the room to be tested-it will suspend settled dust so its mould activity can be characterised, and has previously been shown to be strongly correlated to the presence of visible mould and other moisture induced problems within the space [11]. In this study, an active air sampling strategy was adopted for its ability to rule out the impact of the prior disturbance (or lack of it) within the space on the readings [26–28]. To this end, the air within each room was actively mixed using a Makita blower to mimic some level of activity, standardised by means of blowing duration based on room sizes as follows: 1 min for room sizes up to 10 m 2 , 2 min for room sizes up to 20 m 2 , 3 min for room sizes up to 30 m 2 , and 4 min for larger room sizes.…”

“…Other methods of assessing the mould growth potential include performance models based on dose–response functions developed for certain materials [8–10]. A more detailed analysis of mould presence and intensity in the air or on a surface of a given indoor environment, however, requires direct testing [11]. There are many analytical techniques that can be used to measure mould levels, including culture-based, microscopic, chemical and immunoassay methods, and more recently, polymerase chain reaction (PCR) based methods, each with their respective strengths and biases (see [12] for a review of various techniques).…”

Normal background levels of air and surface mould reserve in English residential building stock: A preliminary study towards benchmarks based on NAHA measurements

“…Within this framework, this study aims to establish normal background levels of mould in order to improve the decision-making process as to when a given indoor environment may be in need for remediation by identifying the ranges common to normal, non-water-damaged buildings without visible mould To this end, a testing protocol previously reported by Aktas et al [11,12] was used, which showed that surface and air sampling should be combined to identify local mould problems, and that an active (aggressive or activated) air sampling strategy, i.e. sampling actively mixed air, better represents indoor mould concentrations than a passive sampling approach, i.e.…”